program Area;

{$APPTYPE CONSOLE}

uses
  SysUtils;
var
  x1, x2, x3, y1, y2, y3, S: integer;

begin
  Write('x1=');
  readln (x1);
  Write('y1=');
  readln (y1);
  Write('x2=');
  readln (x2);
  Write('y2=');
  readln (y2);
  Write('x3=');
  readln (x3);
  Write('y3=');
  readln (y3);
  S:=Abs(((x1-x3)*(y2-y3)-(x2-x3)*(y1-y3)) div 2);
  write('S = ');
  write(S);
  readln;
end.
